Scada, communications network and intelligent RTUs upgrade the monitoring and control facilities of the Nelson Mandela Municipality sewage network.
Utilities with a large number of outstations generate vast quantities of data, which have to be processed using sophisticated control and communication techniques.
Project overview
The Nelson Mandela Metropolitan Municipality in the Eastern Cape controls the water and sewage utilities for Port Elizabeth and its environs, a service area with a radius of about 35 km. A burgeoning population and the large-scale development of the Koega Project underlined the need for more efficient management of the sewage treatment works in the area. The project, involving the upgrade of the control facilities in the sewage network, was divided into two phases, the first involved the upgrade of the treatment works, also known as the 'Fish Water Flats' and the second involved the remote monitoring of the pump stations.
Fish Water Flats WWTW
The upgrade of the scada and telemetry components of the Fish Water Flats sewage treatment works was awarded to Service Electrical. SSE Data Networks is the subcontractor providing the telemetry equipment Citect scada and communications backbone. The project involved the installation and commissioning of a Citect scada at the control room and four remote SSE RTU-10s to monitor and control the inlet works, aeration ponds and clarifiers.
The control room scada system updates in realtime, and data such as level, flow, alarm and motor run hours are automatically logged and trended. The system allows for operator intervention should manual override be required. The scada configuration involved an initial 4000 tags in the first phase; this will increase to approximately 8000 tags in the future.
The remote RTU-10s communicate via wireless LAN to a Citect server and five display clients at the works control room. In this harsh environment, one of the major benefits of the wireless LAN is that future RTUs will be able to be installed without having to run network cables back to the control room.
SSE RTU-10s have powerful programmable logic controllers to control plant in the field. They also have a powerful user interface to enable programming of the RTU and to allow the operator to set up the preferred communications means through the communications orchestrator. The RTUs support wireless LAN, radio, Ethernet, USB, fibre optic, GRPS and conventional cellphone communications.
Raw sewage pumpstation network
System overview
The RTUs and scada employed at the Fish Water Flats sewage treatment works are the same as those employed by the Metropole's pump station telemetry system. In 2002, the scada and telemetry was awarded to SSE Data Networks of Cape Town, which involved monitoring sump alarms, levels and pump status at 70 remote sewage pump stations. The system makes use of radio communications between the master station and remote stations. SSE Data Networks was responsible for the project management, project architecture, communications analysis and configuration of the scada system. The fact that the FWF WWTW and the pumpstation network are now all operating off the same scada, communications and telemetry platform, means that the treatment process and the raw sewage pumping process can be integrated seamlessly. Future management information systems will process the data aggregated by both the WWTW and the raw sewage pumpstations to provide value data for planning ahead as the network grows.
System components
The pumpstation system and the FWF WWTW is based on Citect scada Version 6 with Microsoft Windows XP as the operating system while an SSE RTU-10 telemetry system monitors and controls the 70 pump stations. Data being logged includes flows, pipe pressure and sump levels. The SSE RTU-10 is OPC compliant allowing connectivity to all OPC-compliant Citect scada.
The Process Analyst component of the Citect scada package allows operators to analyse the cause of any process disturbances by bringing together trend and alarm data, traditionally stored separately. The operator can thus compare pump run times, pump fault alarms, flow rates and valve settings on a single integrated display instead of having to look at four different sources of information. This saves time, improves productivity and lowers operating costs. All data is stored in a single global database to simplify software management.
Citect's system architecture features and scalability capabilities will make it easy to implement future plant upgrades and expansions without having to modify existing hardware or software. Changes are implemented at a central point and are immediately updated at all Citect stations. This ensures that uniform, consistent and latest plant information is available to all Citect stations at any time.
Two redundant 5000 I/O Citect servers provide operational and statistical information from a central control room situated at the Nelson Mandela Metropole headquarters. Operations include pump trip, alarms, sump levels and intrusion alarms. The statistical data will provide valuable information for future planning of demands brought about by domestic and industrial growth.
Two display clients - situated in different locations - provide full functionality communicating over wireless network to the servers in the central control room.
MDS Digital Data Radios (imported by SSE Data Networks) provide the medium for the wide area network. MDS radios have a faster key-up time (7 ms) and higher data rate (4800 baud) than analog radios (typically 150 ms at 1200 baud). Data from the sewage outstations is sent to the Citect scada master station, which is able to refresh polled data from the 70 outstations (2000 I/O points) in about 80 to 120 seconds.
Telemetry hardware for the project included a repeater at the central station. The computer and scada included three high-spec PCs on a network. The cabling requirements for the central hardware comprised 2 x RS232 (digital radio data) and one LAN link (to WAN link to remote PC). A problem arose when the cabling became too long for standard RS232 specification (9th floor to 13th floor) and was compounded when the central station was moved to the 17th floor of the adjacent building.
SSE Data Networks selected the SAN People EtherPad Duo to provide the serial connectivity solution. The Duo links two serial ports to a standard TCP/IP LAN. In this application, one Duo re-directs the PC's RS232 ports to an IP address on the network while the other is connected to the LAN at that IP address, and re-creates the RS232 Ports at the remote point.
Using this method, the cabling between the PCs and the hardware of the central station has been reduced to one UTP LAN cable. Furthermore, with the move of the central station to the adjacent building, the municipal LAN could be used for that link as well. This eliminated the need for any cabling, and allowed the central station and the PCs to be located anywhere in the municipal area.
A further benefit of using the EtherPADs in this system implementation is that the two main scadas can be operated in 'hot standby'. This is because no RS232 cables need be moved from one PC to another, the scadas are on-line at all times. Further, because the municipality has a permanent Internet connection, SSE Data Networks is able to connect to the system directly, via the Internet, from Cape Town, and this way offer online software support.
The SSE RTU-10 and SAN People Duo are manufactured to IS0 9000 standards and can be used in a number of applications.
Summary
The sewage network is the largest sewage telemetry contract to be put out to tender for many years in the Eastern Cape, and is almost certainly the largest of its kind to be installed under one contract. SSE RTUs and Citect scada are an ideal combination and have the automation ability to cater for the future demands of this high profile sewage network works.
At the recent system handover, held in August 2005, Wastewater Conveyance Manager, Johan Joubert, commended all involved on the progress to date. Due to the size of the network, SSE Data Networks has established a branch office in Port Elizabeth to provide local support and maintenance back-up.
Professional team
Client: Nelson Mandela Metropole.
Consultants: Wolhuter & Associates, CA Du Toit, Steward Scott.
Contractors: SSE Data Networks, Service Electrical.
Scada vendor: Citect.
Telemetry vendor: SSE.
For more information contact Clive Maasch, SSE Data Networks, 021 552 0420 [email protected], Niconette du Toit, Citect, 011 699 6600, [email protected]
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